Quite generally, an electric igniter for artillery ammunition serves to ignite the primer charge of such ammunition. It comprises a metal casing holding an initiator charge associated with an electric resistor. The resistor is permanently electrically linked to one of the two terminals of a DC source via said casing and is further electrically linked to a contactor which is insulated from the casing and connectable at will with the other terminal of said DC source. Upon the establishment of such contact, the electric resistor is heated whereby said initiator charge is ignited and ignites in turn said primer charge, usually via a booster charge.
By one known method, the initiator charge is intimately mixed witha particulate electric conductor material such as, for example, graphite powder or a metal powder while by another known method an electric wire of such resistance that it glows upon the passage of the design current therethrough extends in contact with the initiator charge.
Both these methods suffer from relatively high spreads of the ignition time and from relatively long ignition times, or less than optimum trade-off of both ignition time and safety. These drawbacks give rise to serious disadvantages which may become prohibitive in modern computerized gunnery.
To overcome some of these problems there have been designed and there are known electric igniters of the kind specified which comprise an electric ignition element in the form of an insulating carrier body, for example of ceramic material, bearing two electric conductors linked by a resistor bridge. In such elements said conductors and bridge are applied to the carrier body by known techniques such as printing or thin layer application.
In modern battle fields there prevails an abundance of electromagnetic radiation, mainly in consequence of telecommunications and radar of various kinds. This radiation gives rise to hazards referred to in the art as HERO (Hazards of Electromagnetic Radiation to Ordnance) in that it induces in the igniters via said contactor spontaneous radio frequency (RF) currents liable to initiate explosion of the ammunition. It has accordingly been realized before that special means are required in order to suppress the formation of induction currents in said igniters. A solution of the problem is described in German Patent specification DE-Al-3502526. In accordance with that disclosure, the imprinted or applied circuit of an electric ignition element is shaped in a complicated tortuous form so as to constitute itself a high frequency filter in consequence of its own increased inductance and capacitance. However, apart from the fact that the formation of the required complicated conductor patterns in such elements is relatively costly, it has been found that such igniters are inapplicable to armoured vehicle artillery. In such vehicles the voltage supply is inherently low and by some standards ignition at 2.1 amp is required. On the other hand because of HERO hazards there should be no firing at 1 amp and this leaves a rather narrow margin of 1.1 amp between NO FIRE and ALL FIRE. It is thus one object of the present invention to provide a reliable electric igniter assembly of the kind specified in which the margin between the current intensities for "NO FIRE" and "ALL FIRE" can be kept low while the HERO hazards are strictly avoided.
It is a further object of the present invention to provide an electric igniter assembly of the kind specified which affords safety against spontaneous initiation in consequence of static electric discharge from the operator.
A further problem encountered in artillery ammunition with an electric igniter assembly of the kind specified are hazards resulting during a firing cycle from rearward bursting combustion gases whilst the ammunition is still in the barrel. These gases penetrate the electric igniter assembly via the voids left in consequence of the combustion of the initiator and booster charges and may deform the base portion of the igniter to an extent that it will interfere with the extraction of the empty shell and accordingly also with the reloading of the gun and give rise to malfunctioning of the firing system. It is therefore a further object of the present invention to overcome this problem and provide an electric igniter assembly of the kind specified in which any rearward bursting combustion gases or materials are prevented from reaching the assembly's base portion.